Wireless communication systems have developed through various generations, including a first-generation analog wireless phone service (1G), a second-generation (2G) digital wireless phone service (including interim 2.5G networks) and third-generation (3G) and fourth-generation (4G) high speed data/Internet-capable wireless services.
More recently, Long Term Evolution (LTE) has been developed by the 3rd Generation Partnership Project (3GPP) as a radio access network technology for wireless communication of high-speed data and packetized voice for mobile phones and other mobile terminals. LTE has evolved from the Global System for Mobile Communications (GSM) system and from derivatives of GSM, such as Enhanced Data rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), and High-Speed Packet Access (HSPA).
In North America, wireless communications systems, such as LTE, use a solution for Enhanced 911, or E911, that links emergency callers with the appropriate public resources. The solution attempts to automatically associate the caller, i.e., the caller's user equipment (UE), with a specific location, such as a civic address or geographic coordinates. Automatically locating the caller with high accuracy (e.g., with a distance error of 50 meters or less) and providing the location to a Public Safety Answering Point (PSAP) can increase the speed with which the public safety side can locate the required resources during emergencies, especially where the caller may be unable to communicate his/her location (e.g. does not know the location or is unable to speak adequately).
To locate a UE geographically, there are several approaches. One is to use some form of terrestrial radio location based on measurements made by a UE of signals transmitted by wireless network base stations and access points (APs). In cases where a measured base station is remote from a UE (e.g. several miles or more distant) or where there is strong interference from transmissions from other base stations, a UE may employ coherent or non-coherent integration over a period of time (e.g. 1 millisecond (ms) up to 100 ms) to acquire and measure a suitable reference signal from the base station. As is well known in the art, coherent integration, in which both the phase and amplitude of a signal are accumulated over time, can enable a better signal to noise ratio (S/N) and more accurate measurements—e.g. of a weak signal or a signal with strong interference. But, as may be observed, coherent integration may be dependent on accurate knowledge of the frequency and coding of the measured signal and may perform worse than non-coherent integration, in which just the power of a signal is accumulated over time, when frequency and/or coding are not precisely known. For example, coherent integration may perform worse than non-coherent integration for a UE that uses a frequency (or clock) source for integrating measurements that differs from the carrier frequency of the base station being measured (e.g. by a few parts per million (ppm)). In some situations, a UE may not know whether its frequency source is of sufficient accuracy to make coherent integration effective or whether greater measurement accuracy could be achieved by using non-coherent integration. Systems and methods that enable a UE to determine when to use coherent integration versus non-coherent integration to achieve improved or optimum measurement accuracy may thus be of benefit.